1. Field of the Invention
The present invention relates, in general, to a gantry crane of the type having rubber tires, commonly used for materials handling, and particularly for handling large, bulky loads such as containerized freight.
2. Information Disclosure Statement
The rubber tire gantry cranes in present use typically are provided with a large framework which includes upstanding columns at the four corners thereof, sill beams disposed on opposite sides of the frame and extending between adjacent pairs of columns, and at least one control cab for controlling the movements of the hoisting mechanism for the grappler mechanisms that engage the load. Also, current gantry cranes have sill beams which are typically straight members and disposed at a level which is above the tires of the crane. Control cabs on current gantry cranes have fixed cabs in two possible locations. The cab may be located below the sill beam near ground level or above the sill beam at some fixed height. The primary disadvantage to a fixed cab is that visibility in certain situations is greatly obstructed. To address this problem, some gantry cranes are manufactured with a low cab under one sill beam and a high cab over the opposite sill beam to allow operators more flexibility during operation. However, the operator is only able to operate from one control cab at a time and must walk to the opposite side of the crane to switch cabs. He must also climb a tall ladder to access the cab. Such dual cabs increase complexity of controls and increase maintenance costs. Additionally, in current gantry cranes, the cabs do not have an unobstructed 360.degree. visual field for the operator.
Having an unobstructed 360.degree. view for the operator in the control cab is important for a number of reasons, including: (1) To give the operator complete all around visibility without any impediments to prevent running over people with the crane, and (2) To permit the operator to look in all directions for maneuvering the crane and the grapplers during the picking up and discharging of the load.
A preliminary patentability search in Class 212, subclasses 218, 219 and 220, and Class 414, subclasses 459 and 460, produced the following patents, some of which may be relevant to the present invention:
Smith, U.S. Pat. No. 3,957,165, issued May 18, 1976; Appleman et al, U.S. Pat. No. 4.,378,072, issued Mar. 29, 1983; Lanigan et al, U.S. Pat. No. 4,667,834, issued May 26, 1987; Pippen et al, U.S. Pat. No. 4,747,745, issued May 31, 1988; Ishige et al, U.S. Pat. No. 4,838,438, issued Jun. 13, 1989; and Lanigan, Jr. et al, U.S. Pat. No. 4,877,365, issued Oct. 31, 1989.